# Icosagonal number

Given a number n, the task is to find the nth Icosagonal number.
An Icosagonal number is the 20-gon is a twenty-sided polygon. The number derived from the figurative class. There are different pattern series number in this number. The dots are countable, arrange in a specific way of position and create a diagram. All the dots have a common dots points, all others dots are connected to this points and except this common point the dots connected to their i-th dots with their respective successive layer.

Examples :

Input : 3
Output :57

Input :8
Output :512 Formula for nth icosagonal number: ## C++

 // C++ program to find  // nth Icosagonal number  #include  using namespace std;     // Function to calculate Icosagonal number  int icosagonal_poly(long int n)  {      // Formula for finding      // nth Icosagonal number      return (18 * n * n - 16 * n) / 2;  }     // Drivers code  int main()  {      long int n = 7;      cout << n << "th Icosagonal number :"                 << icosagonal_poly(n);         return 0;  }

## Java

 // Java program to find  // nth Icosagonal number     import java.io.*;     class GFG {         // Function to calculate Icosagonal number     static int icosagonal_poly(int n)  {      // Formula for finding      // nth Icosagonal number      return (18 * n * n - 16 * n) / 2;  }     // Drivers code             public static void main (String[] args) {            int n = 7;             System.out.print (n + "th Icosagonal number :");      System.out.println(icosagonal_poly(n));      }  }  // This code is contributed by aj_36

## Python 3

 # Python 3 program to find   # nth Icosagonal number     # Function to calculate  # Icosagonal number  def icosagonal_poly(n) :             # Formula for finding      # nth Icosagonal number      return (18 * n * n -              16 * n) // 2    # Driver Code  if __name__ == '__main__' :      n = 7     print(n,"th Icosagonal number : ",                      icosagonal_poly(n))     # This code is contributed m_kit

## C#

 // C# program to find  // nth Icosagonal number  using System;     class GFG  {     // Function to calculate  // Icosagonal number  static int icosagonal_poly(int n)  {      // Formula for finding      // nth Icosagonal number      return (18 * n * n -               16 * n) / 2;  }     // Driver code  static public void Main ()  {         int n = 7;     Console.Write(n + "th Icosagonal " +                          "number :");  Console.WriteLine(icosagonal_poly(n));  }  }     // This code is contributed by ajit

## PHP

 

Output :

7th Icosagonal number :385


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